Several different types of neutron dosimeters are available for detecting the exposure level of personnel to moderate and high energy neutrons, which are of relatively low cost and compact to enable them to be worn by personnel. One type of dosimeter is the NTA (nuclear track emulsion) film which includes a photographic-type emulsion lying on a plastic base. The film can be developed and the resulting tracks counted to determine the neutron exposure. However, such dosimeters are sensitive primarily to high energy neutrons of more than 0.7 MeV (million electron volts), in that few tracks are produced for moderate energy neutrons of under about 0.7 MeV. Another type of neutron dosimeter is the TLD (thermoluminescence dosimeter)-albedo type which includes a sheet or crystaline chip of neutron-to-alpha particle conversion material such as .sup.6 Li material. Neutrons striking the conversion material deposit energy in it, and when the sheet is later heated, it emits light which can be recorded to provide an indication of the neutron exposure. However, the material is sensitive primarily to moderate energy neutrons of less than about 1 MeV, such as albedo neutrons generated in the body of a person when he is struck by a high energy neutron.
Another type of neutron dosimeter is the track etch type which utilizes a sheet of dielectric material wherein neutrons produce tracks in the material. One type is the fission track etch dosimeter wherein neutrons striking a foil of fissionable material, produce fission fragments that damage an adjacent sheet of plastic or mica film, with the damage or tracks being visible when the sheet is etched. However, such dosimeters are responsive primarily to high energy neutrons above about 1 MeV. Another type of track etch dosimeter is the recoil track etch dosimeter wherein neutrons strike a sheet of plastic material such as a carbonate to create a track in the sheet, by a process wherein a neutron striking a hydrogen atom causes the emission of an energetic proton that can break the polymer chain of the plastic. Such a dosimeter is also responsive primarily to moderately high-to-high energy neutrons.
In order to determine the exposure level of a person to neutrons, to determine whether the person has received close to the maximum allowable exposure, it is necessary to take into account both moderate and high energy neutrons, and to also take into account the fact that high energy neutrons produce much more biological damage than moderate energy neutrons. One technique for accomplishing this is to use a dosimeter that includes both high and moderate energy detector portions. The dose of moderate energy neutrons is converted into its biological equivalent dose, the dose of high energy neutrons is converted into its biological equivalent dose, and the sum of the biological equivalent doses is taken to determine whether it is close to the maximum allowable equivalent dose. However, the need to examine the record made on two separate devices, and to convert and then to add the resulting measurements, adds to the complexity of the measuring process and increases the chances for errors. A neutron dosimeter that enabled a single measurement to be taken to indicate the biological equivalent dose, as to determine whether the maximum allowable dosage has been reached or not, would simplify the monitoring of neutron exposure of personnel.